A beam of high-energy particles can be used to deliver a therapy to a patient, for example, as medical treatment for a patient's cancer. Particles in the beam (e.g., protons) can have energies greater than 20 MeV, for example, between 70 MeV and 250 MeV. The particles can be generated in a particle accelerator and delivered to a patient at a treatment station where the particle beam emanates from an irradiation nozzle. The nozzle directs the beam at the patient on a support, for example, an adjustable gurney or chair that holds the patient in position relative to the particle beam. The depth of particle penetration and the position of the particle beam may be varied in order to treat a three-dimensional volume within a patient. Depth control can be achieved by varying the energy of the particles. A gantry is used to rotate the irradiation nozzle about the patient to irradiate the desired volume within the patient from different angles.
A configuration of a particle therapy system 100 is shown in FIG. 1A. The particle therapy system 100 receives a particle beam 114, for example, a proton beam, from a particle beam source (not shown), such as a particle accelerator. The particle beam 114 is transported from the particle beam source via a beam transport system (not shown) that provides the beam 114 to the gantry 108 for irradiating a patient 102. The beam transport system can include a vacuum tube and beam control components, such as, quadrupole magnets that focus the particle beam and dipole magnets that deflect the particle beam.
The particle beam 114 enters the gantry 108 via a rotating vacuum seal 112. Within the gantry 108, the particle beam can follow a serpentine path to an irradiation nozzle 122, which redirects the particle beam along path 110 for irradiation of the patient 102. Magnets 118 and 120 within gantry 108 redirect the particle beam from the vacuum seal 112 to the irradiation nozzle 122. The magnets 118 and 120 rotate with the irradiation nozzle 122, while the relative positions (i.e., the vertical distance perpendicular to axis 116 and the horizontal distance parallel to axis 116 between the magnets 118 and 120) between magnets 118 and 120 remain otherwise fixed even though their orientation changes.
A patient support 104 positions the patient 102 aligned with a rotation axis 116 of the gantry 108. The irradiation nozzle 122 is rotated around the rotation axis 116 by the gantry 108 to irradiate the treatment volume within the patient from different angles. The gantry 108 can be rotated such that the beam 110 hits the treatment isocenter of the patient 102 without the need to change magnetic field strengths of the magnets. For example, as illustrated in FIG. 1B, the gantry can move the irradiation nozzle 122 from a vertical position 130 above the patient (e.g., 0° rotation), to a horizontal position 132 (e.g., 90° rotation), to a vertical position 134 below the patient (e.g., 180° rotation), to another horizontal position 136 on an opposite side of the patient (e.g., 225° rotation), and to various points in between. To accommodate the rotation of the irradiation nozzle at a constant radius with respect to the patient 102, the patient support 104 holds the patient 102 at an elevated position above the floor 106. Alternatively or additionally, the gantry 108 may have a portion that lies below the floor 106 to minimize or at least reduce the height at which the patient 102 is positioned.
As a result of the above described operation, particle therapy gantries can be heavy and have a footprint significantly larger than conventional photon therapy gantries. Such known gantry designs require complex and bulky structures, in particular in order to allow the gantry to be rotated through a full 360° around the irradiation object.